Method of manufacturing a PCB having improved cooling

ABSTRACT

An improved cooling of an electronic component loaded to a printed circuit board, wherein the PCB comprises at its upper side at least one electronic component, and at least one heat conducting member inserted into a through-hole of the PCB, wherein the HCM extends from the upper side to the lower side of the PCB and has a thermal contact to the components.

CROSS-REFERENCED APPLICATIONS

The present disclosure is a Divisional Application of U.S. patentapplication Ser. No. 10/814,041, filed on Mar. 31, 2004 now U.S. Pat.No. 7,151,229.

BACKGROUND

The present disclosure relates to printed circuit boards (PCB), whichusually are loaded with numerous electrical components, e.g., integratedcircuits (IC). During operation these components generate heat, whichhas to be removed from the components in order to improve performanceand extend the lifetime of the components. Current electronic devicesare usually provided with several PCBs and comprise a cooling deviceproviding a heat sink for removing the heat from the criticalcomponents.

SUMMARY

It is an object of the present disclosure to provide an improved way ofcooling an electronic component mounted to a PCB.

The disclosure suggests a heat conductive member (HCM) for eachcomponent to be cooled, wherein the HCM is arranged in a through-hole,which is provided in the PCB, wherein the HCM is thermally contactedwith the component and extends within the through-hole from the upperside of the PCB to the lower side of the PCB. Therefore, the HCMtransmits heat from the component, which is arranged at the upper sideof the PCB, to the lower side of the PCB by locally improving thethermal conductivity of the PCB. At the lower side of the PCB the HCMcan be contacted with an appropriate heat sink, e.g. a cooling device.Thus, the effectiveness of cooling the component can obviously beimproved. The HCM is made of an appropriate thermally conductivematerial, e.g. brass, copper or a copper-alloy. The HCM comprises asubstantially planar top portion and tapered or recessed bottom portionso that substantially only the areas turned away from the top side ofthe HCM are deformed during a force fitting of the HCM into thethrough-hole.

In case a heat sink is used, the invention allows providing almostdirect contact with the respective components, thus providing improvedeffectiveness of such cooling.

According to a preferred embodiment, the through-hole is positionedcentrally underneath the component to be cooled, wherein a topside ofthe HCM is directly thermally contacted with a bottom side of thecomponent. By directly contacting the component to the HCM heat lossesin the thermal path can be reduced. It should be clear that between thebottom side of the component and the topside of the HCM any appropriatethermally conductive contacting substances like a solder can be arrangedin order to improve the thermal contact in-between HCM and component.Preferably the bottom side of the component is provided with aheat-emitting surface, e.g. a metallic surface, improving the heatexchange between the component and the HCM.

To improve the effectiveness of the thermal flow the topside of the HCMmay be plainly aligned with the upper side of the PCB and/or a bottomside of the HCM may be plainly aligned with the lower side of the PCB.With help of these features the direct contact and thus the thermalconductivity between the topside of the HCM and the bottom side of thecomponent and/or between the bottom side of the HCM and a topside of aheat sink can be improved. These features also simplify serialproduction of the PCB and of electrical devices provided with such PCBs.

According to manufacturing tolerances the thickness of the PCB, whichconsists usually of multiple layers, may vary in a relatively widetolerance range. To provide a substantially exact planar alignmentbetween the top side of the HCM and the upper side of the PCB andbetween the bottom side of the HCM and the lower side of the PCB apreferred manufacturing method proposes to provide the HCM before it isforce fitted into the through-hole with an origin shape, in which thedimension between the top side and the bottom side of the HCM is largerthan the thickness of the PCB. Thus, the force fitting can be performedto press the HCM into the through-hole as long as the respective sidesof HCM and PCB are aligned to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and many of the attendant advantages of the presentinvention will be readily appreciated and become better understood byreference to the following detailed description when considered inconnection with the accompanying drawings. Features that aresubstantially or functionally equal or similar will be referred to withthe same reference sign(s).

FIG. 1 to 3: depict cross sections through a PCB according to theinvention in an area provided with a component to be cooled at differentconfigurations,

FIG. 4 to 8: depict cross sections as shown in FIG. 1 to 3 at differentmanufacturing states.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 to 3 a Printed Circuit Board 1 (PCB 1) according tothe invention is provided with at least one electrical component 2. Thiscomponent 2 generates heat, when it is in an operational mode. Thecomponent 2 e.g. can be a microprocessor or another arbitrary IC. ThePCB 1 has an upper side 3 on which the component 2 is arranged with itsbottom side 4 down. This bottom side 4 of the component 2 is preferablyprovided with a heat-emitting surface and e.g. is made of an appropriatemetal or metal alloy. This heat-emitting surface is preferably directlyconnected to a semiconductor arranged inside of a housing of thecomponent 2.

The PCB 1 consists of several layers 5 of a suitable substrate material,thus the PCB 1 has a multilayer design. These layers 5 are usuallyprovided with printed circuits. Underneath the component 2 the PCB 1 isprovided with a through-hole 6 extending from the upper side 3 to alower side 7 of the PCB 1. In this through-hole 6 is—according to theinvention—inserted a Heat Conductive Member 8 (HCM 8) having a topside 9and a bottom side 10. The HCM 8 is with its top side 9 thermallycontacted with the bottom side 4 of the component 2 (e.g. by a standardsoldering process) and extends within the through-hole 6 form the upperside 3 of the PCB 1 to the lower side 7 of the PCB 1. The HCM 8 is madeof a material that is especially appropriate for heat transmission e.g.copper or a copper alloy.

When the PCB 1 is provided with a heat sink 12 of a cooling device 13(both symbolized by dashed lines) the heat sink 12 is arranged at thelower side 7 of the PCB 1. Preferably, the heat sink 12 with its topside14 directly contacts the lower side 7 of the PCB 1. Since the HCM 8extends to the lower side 7 of the PCB 1 it thermally contacts thetopside 14 of the heat sink 12 with its bottom side 10. Therefore, theHCM 8 provides a very effective heat-transmitting path directlytransporting heat from the component 2 by means of the HCM 8 to the heatsink 12. With help of the HCM 8 the cooling of the component 2 can behighly improved. Thus, the performance and the lifetime of the component2 can be improved accordingly.

It may be suitable to arrange any appropriate thermally conductivecontacting substance like a solder between the bottom side 4 of thecomponent 2 and the top side 9 of the HCM 8 and, respectively, betweenthe bottom side 10 of the HCM 8 and the top side 14 of the heat sink 12in order to improve the direct thermal contact between HCM 8 andcomponent 2 and, respectively, between HCM 8 and heat sink 12.

Referring to the FIG. 1 to 3 (see also FIG. 4 to 8) the HCM 8 isprovided with a top portion 15 and a bottom portion 16. The top portion15 has a centrally closed disc shape and comprises the topside 9 of theHCM 8. Therefore, the topside 9 of the HCM 8 has a large surface forimproved contact with the bottom side 4 of the component 2. At an outeredge 17 the top portion 15 is provided with several projections 18 whichradially extend from the outer edge 17. These projections 18 can beprovided as a tooth system or as a knurl. When the HCM 8 is insertedinto the through-hole 6 the projections 18 penetrate into an inner wall19 of the PCB 1, said inner wall 19 enclosing the through-hole 6.Therefore, the projections 18 affix the HCM 8 to the PCB 1.

The bottom portion 16 has a centrally open ring shape and comprises thebottom side 10 of the HCM 8. The bottom portion 16 extends from the topportion 15. Before inserting the HCM 8 into the through-hole 6 the HCM 8has an origin shape shown in FIG. 4 to 6. In this origin shape thebottom portion 16 has a truncated conical profile, which tapers with thedistance to the top portion 15. After insertion of the HCM 8 into thethrough-hole 6 the bottom portion 16 is plastically deformed.

The HCM 8 preferably has a substantially rotationally symmetrical shape.Consequently, the through-hole 6 has a cylindrical shape. In aconvenient embodiment the HCM 8 is made as a one-piece element.

With respect to the FIG. 4 to 8 a preferred method for manufacturing thePCB 1 is described in the following.

According to FIG. 4 the HCM 8 having its origin shape is positioned on afirst pressing tool 20 of a pressing device 21. The first pressing tool20 preferably has a planar surface and is provided with a centeringmandrill 22, which is longitudinally adjustable in the center of thefirst pressing tool 20. In the state of FIG. 4 the centering mandrill 22projects from the first pressing tool 20. The HCM 8 is arranged on thefirst pressing tool 20 such that the centering mandrill 22 penetratesinto a central cavity 23 of the HCM 8, said cavity 23 is encircled bythe ring-shaped bottom portion 16. The centering mandrill 22 urges theHCM 8 into a predetermined centered position as could be seen in FIG. 5.Is should be clear that a top 24 of the centering mandrill 22 can haveany appropriate shape supporting the centering function. E.g. the top 24also can have a truncated conical and tapering shape.

After positioning the HCM 8 relative to the first pressing tool 20 thePCB 1 already provided with the through-hole 6 is positioned relative tothe first pressing tool 20, see FIG. 5, wherein the PCB 1 has its lowerside 7 turned to the HCM 8 and to the first pressing tool 20. It isclear that positioning of PCB 1 and HCM 8 can be performed in the otherorder or simultaneously. At the end of this positioning procedure theHCM 8 is aligned with the through-hole 6.

After aligning the HCM 8 and the through-hole 6 the HCM 8 becomes pressor force fitted into the through-hole 6 by means of pressing forces. Tothis aim the pressing device is provided with a second pressing tool 25co-operating with the upper side 3 of the PCB 1, see FIG. 6. The secondpressing tool 25 preferably has a planar surface, too, which extendsparallel to the surface of the first pressing tool 20. The pressingtools 20 and 25 are then pressed towards each other according to anarrow 26. The pressing direction extends perpendicular to the planarsurfaces of the pressing tools 20, 25. Simultaneously the centeringmandrill 22 gets retracted into the first pressing tool 20 according toan arrow 27. As can lucidly be seen in FIG. 6 the outer diameter of thetop portion 15 of the HCM 8 is due to the projections 18 larger than theinner diameter of the through-hole 6. Therefore, the projections 18penetrate radially into the inner wall 19 of the through-hole 6, whilethe HCM 6 is pressed into the through-hole 6. In doing so the projection18 deform the inner wall 19 and act like barbs intensively anchoring theHCM 8 in the PCB 1.

According to a preferred embodiment of the present invention the originshape of the HCM 8 is chosen in a way that a thickness 28 of the HCM 8is larger than a thickness 29 of the PCB 1, see FIG. 5. The thickness 28of the HCM 8 is the distance between its topside 9 and its bottom side10. Accordingly, the thickness 29 of the PCB 1 is the distance betweenits upper side 3 and its lower side 7. As the PCB 1 is of a multilayerdesign the thickness 29 of the PCB 1 naturally varies within arelatively large tolerance range comprising a maximum value and aminimum value for the thickness or distance 29. Preferably, the distanceor thickness 28 of the HCM 8 is in the origin shape of the HCM 8 largerthan the maximum value of the aforementioned tolerance interval.

As can be seen in FIG. 7 the pressing tools 20, 25 are pressed togetheruntil the top side 9 of the HCM 8 abuts against the second pressing tool25. Since the thickness 28 of the HCM 8 at this state of the procedurestill is larger than the thickness 29 of the PCB 1 the progressingmovement of the pressing tools 20, 25 deforms the HCM 8 and creates thefinal shape of the HCM 8. The movement of the pressing tools 20, 25 isin progress as long as both pressing tools 20, 25 are in contact withthe respective sides 3, 7 of the PCB 1. Consequently, the pressing tools20, 25 plastically deform the HCM 8. After the pressing process the HCM8 has the same thickness 29 as the PCB 1. Therefore, the topside 9 ofthe HCM 8 is planarly aligned with the upper side 3 of the PCB 1 and thebottom side 10 of the HCM 8 is planarly aligned with the lower side 7 ofthe PCB 1. By this the thickness dimension of the HCM 8 is calibrated tothe thickness of the PCB 1 independent of the thickness value of the PCB1 inside its tolerance range.

The closed disc-shaped top portion 15 is very solid and effects that theplane topside 9 of the HCM 8 is not or essentially not deformed duringthe force fitting of the HCM 8 into the through-hole 6. The truncatedconical and tapering profile of the open ring-shaped bottom portion 16effects that the areas turned away from the top side 9 of the HCM 8 arefirst to be deformed and the areas near the top portion get not orhardly deformed.

As can be seen clearly in FIGS. 7 and 8 the HCM 8 is designed in a waythat after force fitting the HCM 8 into the through-hole 6 a ring-shapedradial gap 11 is provided between the bottom portion 16 and the innerwall 19. According to this design feature damaging of the PCB 1 can beprevented while performing the force fitting of the HCM 8 into thethrough-hole 6. The force fitting of the HCM 8 can be performed bycontrolling the movement of the pressing tools 20, 25. In a preferredembodiment the press fitting of the HCM 8 is force controlled, i.e. thepressing tools 20, 25 are pressed together with a predetermined constantpressing force high enough for plastically deforming the HCM 8 and toolow for damaging the PCB 1. Therefore, the controlling is independentfrom the varying thickness 29 of the PCB 1.

After completing the force fitting of the HCM 8 into the through-hole 6the pressing tools 20, 25 get retracted and the PCB 1 can be removed outof the pressing device 21. Afterwards the PCB 2 can be provided with thecomponent 2, wherein an additional thermally contacting substance may beapplied between HCM 8 and component 2 to improve plane contact alonglarge surfaces.

Although the FIG. 4 to 8 only show the insertion of a single HCM 8 intoits respective through-hole 6 it is clear that the insertion process canbe performed such that at least two or in particular all HCMs 8 of aspecific PCB 1 can be inserted simultaneously into their respectivethrough-holes 6.

FIG. 1 to 3 depict three different configurations, which may occur byinserting the HCM 8 into the through-hole 6 of the PCB 1. In FIG. 1 thePCB 1 shows the minimum value for its thickness 29. Consequently, theforce fitting of the HCM 8 leads to a maximum deformation of the HCM 8or its bottom portion 16, respectively. As it can be seen, thedimensions of the origin shape of the HCM 8 are preferably chosen in away that even in this border case the gap 11 can be provided.

FIG. 3 shows the other border case, wherein the thickness 29 of the OCB1 has its maximum value. Thus, the force fitting of the HCM 8 leads to aminimum deformation of the bottom portion 16 of the HCM 8. Preferably,the dimensions of the origin shape of the HCM 8 are chosen such thateven in this border case still occurs a deformation of the HCM 8.

Finally FIG. 2 shows a configuration between the border cases of FIGS. 1and 3 leading to a medium deformation of the HCM 8 during the forcefitting procedure.

1. Method for manufacturing a printed circuit board (PCB), the methodcomprising the steps of: providing the PCB with at least onethrough-hole, inserting a heat conductive member (HCM) into thethrough-hole, wherein the HCM comprises a substantially planar topportion and tapered or recessed bottom portion, force fitting the HCMsuch that substantially only the areas turned away from the top side ofthe HCM are deformed, and providing the PCB with an electrical componentthat is thermally coupled with the substantially planar top portion ofthe HCM, the HCM providing a heat-transmitting path from thesubstantially planar top portion to the tapered or recessed bottomportion.
 2. The method according to claim 1, wherein the press fittingis controlled by force.
 3. The method according to claim 1, comprisingthe steps of: providing the HCM with an origin shape before it is forcefitted into the through-hole, such that in the origin shape a distancebetween the top side of the HCM and the bottom side of the HCM is largerthan a distance between the upper side of the PCB and the lower side ofthe PCB, and performing the force fitting such that the HCM has a finalshape after it is force fitted into the through-hole, such that in thefinal shape the distance between the top side and the bottom side of theHCM is substantially as big as the distance between the upper side andthe lower side of the PCB.
 4. The method according to claim 3, whereinthe origin shape of the HCM is chosen in at least one of the followingways: such that the distance between top side and bottom side of the HCMis larger than the largest value of a manufacturing tolerance range forallowable distances between upper side and lower side of the PCB, andsuch that after press fitting of the HCM into the through-hole aring-shaped gap is provided between a bottom portion of the final shapeof the HCM and an inner wall enclosing the through-hole.
 5. The methodaccording to claim 1, wherein the HCM is provided with a ring-shapedbottom portion which has a truncated conical profile tapering withincreasing distance from a disc-shaped top portion of the HCM.
 6. Themethod according to claim 1, wherein the force fitting of the HCM intothe through-hole is provided by a pressing device comprising a firstpressing tool arranged at one side of the PCB, and a second pressingtool arranged at the opposing side of the PCB, and wherein the secondpressing tool supports the PCB, while the first pressing tool pressesthe HCM into the through-hole as long as the first pressing toolcontacts the respective side of the PCB.
 7. The method according toclaim 6, wherein the first pressing tool is provided with a centeringmandrill projecting from the first pressing tool and penetrating into acenter cavity of the HCM for aligning the HCM with the through-hole, andthe centering mandrill is retracted into the first pressing tool beforepress fitting the aligned HCM into the through-hole.